Conventional culture plates or bottles used for the propagation of cells in vitro are typically manufactured from polystyrene or glass. The routine method for culturing cells includes inoculating the cells into flasks, single culture dishes or multi-well plates, adding a nutrient medium and incubating the cells under controlled conditions. Alternative methods for the in vitro culturing of cells include growing cells in continuously rolling glass or plastic bottles, so that the cells adhere to the wall of a culture vessel beneath continually rotated medium (cells may alternately be grown in fluted roller bottles that have increased inside surface area), or culturing cells on glass or complex polysaccharide beads, tissue segments or in suspension in a suitable culture medium. With all these methods, the culture medium does not exert any deforming stress upon the cells themselves such as would simulate the in vivo stresses applied by tendons, for example, or the cyclic stresses exerted by the heart or lungs on their constituent cells.
One system for the in vitro flexing of cells in culture is documented in Banes, A. J. et al., "A New Vacuum-Operated Stress-Providing Instrument That Applies Static or Variable Duration Cyclic Tension or Compression to Cells In Vitro," J. Cell Sci., 1985. (Related in vitro systems are documented in Somjen, D. et al., "Bone Remodelling Induced by Physical Stress in Prostaglandin E.sub.2 Mediated," Biochimica et Biophysica Acta, 627 (1980) 91-100; Leung, D. Y. M. et al., "A New In Vitro System for Studying Cell Response to Mechanical Stimulation." Experimental Cell Research, 109 (1977) 285-298; Leung, D. Y. M. et al., "Cyclic Stretching Stimulates Synthesis of Matrix Components by Arterial Smooth Muscle Cells In Vitro," Science, 191 (1976) 475-477; Hasagawa et al., "Mechanical Stretching Increases the Number of Cultured Bone Cells Synthesizing DNA and Alters Their Pattern of Protein Synthesis," Calcif Tissue Int, 37 (1985) 431-436; and Brunette, D. M. et al., "Mechanical Stretching Increases the Number of Epithelial Cells Synthesizing DNA in Culture," J Cell Sci, 59 (1984) 35-45.) An improved system for the in vitro flexing of cells is disclosed in U.S. Pat. No. 4,789,601, issued Dec. 6, 1988, to Banes, A. J., U.S. Pat. No. 4,822,741, issued Apr. 18, 1989, to Banes, A. J., and U.S. Pat. No. 4,839,280, issued Jun. 13, 1989, to Banes, A. J.
When cells are flexed in vitro in liquid culture medium, the question arises whether any changes observed (as compared with the same cells grown under static conditions) are caused directly by the flexing of the cell growth substrate or whether such changes are eventuated by secondary currents or turbulence created within the liquid medium as a result of the flexing of the substrate. Obviously, conventional static cell growth cultures cannot provide a "control" in the investigation of this question; neither substrate flexing nor liquid medium movement is present in such systems. Accordingly, a need remains for a cell growth "control" device which can subject its cells to a liquid cell growth media, which media is agitated by the flexing of a separate cell substrate, but can do so without actually flexing the cells it supports.